1. Field of the Invention
The present invention relates to an optical receiver, optical transmitter and optical transceiver.
2. Related Background Art
FIG. 5 is a circuit diagram of a conventional optical receiver. The conventional optical receiver includes a light receiving element 2, an amplifier circuit 4 and a capacitor 8. The light receiving element 2 receives an optical signal, and generates an optical current. The amplifier circuit 4 amplifies the optical current generated in the light receiving element 2, and outputs the amplified optical current. The capacitor 8 is provided to remove noise from a power supply Vcc, which supplies a voltage to the amplifier circuit 4.
In the conventional optical receiver, the power supply Vcc, which supplies the voltage to the amplifier circuit 4, is connected to the light receiving element 2 as well. Therefore, the power supply Vcc not only supplies the voltage to the amplifier circuit 4, but also applies a reverse bias voltage to the light receiving element 2.
FIG. 19 is a schematic diagram of a conventional optical transceiver. The optical transceiver includes a light emitting element 1 and a light receiving element 3 for signal transmission. The light emitting element 1 and the light receiving element 3 can be mounted on a single light-transmitting package.
FIG. 20 is a schematic diagram of another conventional optical transceiver. A light emitting element 1 is disposed on a light receiving element 3. As a result, the optical transceiver is small-sized, and the light emitting element 1 and the light receiving element 3 can respectively transmit and receive signals via the same optical fiber.
As the reverse bias voltage applied to the light receiving element 2 in the conventional optical receiver is made greater, the capacitance and resistance of the light receiving element 2 for high frequency signals become lower. The greater the reverse bias voltage becomes, therefore, the more the optical receiver suits high-rate communication.
In the conventional optical receiver, however, it is impossible to apply to the light receiving element 2 a voltage which is larger than the power supply voltage Vcc supplied to the amplifier circuit 4. In other words, there is a problem that the transmission rate of the optical receiver is limited by a value of the power supply voltage Vcc.
The capacitance of the light receiving element 2 can be reduced by reducing the area of the light receiving element 2. However, reducing the area of the light receiving element 2 causes a problem that the optical current supplied from the light receiving element 2 is reduced and coupling to the optical fiber, which transmits an optical signal, becomes difficult.
Furthermore, in the conventional optical transceiver shown in FIGS. 19 and 20, the light emitting element 1 emits light in response to the forward bias voltage supplied from the power supply, and the light receiving element 3 converts an optical signal to an electric signal in response to the reverse bias voltage supplied from the power supply. Therefore, the light emitting element 1 depends upon the power supply voltage, and the light emitting element 1 cannot be supplied with a voltage exceeding the power supply voltage. The light receiving element 3 also depends upon the power supply voltage, and the light receiving element 3 cannot be supplied with a voltage exceeding the power supply voltage. As a result, the rate of the optical signal, which the light receiving element 3 can receive, is limited by the power supply voltage.
Documents related with the Related Background Art described above are Japanese Patent Laid-Open No. H6-216738 and No. H4-113713.